The investigations proposed for this project are directed toward a functional analysis of conditional stimulus control over visual choice discrimination in young normal and developmentally delayed persons. Emphasis is placed upon understanding principles involved in bringing selection of choice stimuli under conditional control of spoken words and visual samples or standards. Previous research has demonstrated that delayed persons, relatively sophisticated linquistically, can be trained to select one stimulus choice (out of two available choices) in the presence of one spoken word and will subsequently respond away from the trained choice on intermittent presentations of an untrained spoken word. A major portion of the proposed research is directed toward determining the necessary and sufficient conditions for establishing conditional control over choice responding. The investigators are interested in the relationship of the visual standard in a visual match-to-sample task and the incorrect choice stimulus as well as the correct choice stimulus. The data suggests the subject may learn that the incorrect stimulus does not go with a given standard which can be demonstrated by responding away from that stimulus choice whenever that standard is present. These basic laboratory studies are viewed as specifying principles which may be used to improve the technology in applied settings for training the developmentally delayed person.